Hey Invision I dont know if your looking for something a lil more sophisticated but Ive used these testers on my pool and hot tub they always seem to be dead on. check out this link http://cgi.ebay.com/New-pH-Meter-Aqu...QQcmdZViewItem you may also want to check out a pool supply store in your area rather than a grow supply store keep us updated and good luck to ya!!!